ISL28134_14 Datasheet, PDF (16/25 Pages) Intersil Corporation – 5V Ultra Low Noise, Zero Drift Rail-to-Rail Precis Op Amp

ISL28134
Output Phase Reversal
The Output phase reversal is the unexpected inversion of the
amplifier output signal when the inputs exceed the common
mode input range. Since the ISL28134 is a rail-to-rail input
amplifier, the ISL28134 is specifically designed to prevent output
phase reversal within its common mode input range. In fact, the
ISL28134 will not phase invert even when the input signals go
0.5V beyond the supply rails (see Figure 38). If input signals are
expected to go beyond the rails, it is highly recommended to
minimize the forward biased ESD diode current to prevent phase
inversion by placing a resistor in series with the input.
High Gain, Precision DC-Coupled Amplifier
Precision applications that need to amplify signals in the range
of a few µV require gain in the order of thousands of V/V to get a
good signal to the Analog to Digital Converter (ADC). This can be
achieved by using a very high gain amplifier with the appropriate
open loop gain and bandwidth.
In addition to the high gain and bandwidth, it is important that
the amplifier have low V_OS and temperature drift along with a
low input noise voltage. For example, an amplifier with 100µV
offset voltage and 0.5µV/°C offset drift configured in a closed loop
gain of 10,000V/V would produce an output error of 1V and a
5mV/°C temperature dependent error. Unless offset trimming and
temperature compensation techniques are used, this error makes it
difficult to resolve the input voltages needed in the precision
application.
The ISL28134 features a low V_OS of ±4µV max and a very stable
10nV/°C max temperature drift, which produces an output error of
only ±40mV and a temperature error of 0.1mV/°C. With an ultra
low input noise of 210nV_P-P (0.1Hz to 10Hz) and no 1/f corner
frequency, the ISL28134 is capable of amplifying signals in the µV
range with high accuracy. For even further DC precision, some
feedback filtering C_F (see Figure 47) to reduce the noise can be
implemented as a total signal stage amplifier. As a method of best
practice, the ISL28134 should be impedance matched at the two
input terminals. A balancing capacitor of the same value at the
on-inverting terminal will result in the amplifier input impedances
tracking across frequency
100Ω
C_F
1MΩ
+2.5V
A_CL = 10kV/V
ISL28134 SPICE Model
Figure 48 shows the SPICE model schematic and Figure 49 shows
the net list for the SPICE model. The model is a simplified version
of the actual device and simulates important AC and DC
parameters. The AC parameters incorporated into the model are:
1/f and flat band noise voltage, slew rate, CMRR, and gain and
phase. The DC parameters are I_OS, V_OS, total supply current,
output voltage swing and output current limit (65mA). The model
uses typical parameters given in the “Electrical Specifications”
table beginning on page 4. The AVOL is adjusted for 174dB with
the dominant pole at 6.5mHz. The CMRR is set at 135dB,
f = 200Hz. The input stage models the actual device to present an
accurate AC representation. The model is configured for an
ambient temperature of +25°C.
Figures 50 through 63 show the characterization vs simulation
results for the noise voltage, open loop gain phase, closed loop
gain vs frequency, CMRR, large signal 3V step response, large
signal 1V step response, and output voltage swing V_OH/V_OL
±2.5V supplies (no phase inversion).
LICENSE STATEMENT
The information in the SPICE model is protected under United
States copyright laws. Intersil Corporation hereby grants users of
this macro-model, hereto referred to as “Licensee”, a
nonexclusive, nontransferable license to use this model, as long
as the Licensee abides by the terms of this agreement. Before
using this Macro-Model, the Licensee should read this license. If
the Licensee does not accept these terms, permission to use the
model is not granted.
The Licensee may not sell, loan, rent, or license the
macro-model, in whole, in part, or in modified form, to anyone
outside the Licensee’s company. The Licensee may modify the
Macro-Model to suit his/her specific applications, and the
Licensee may make copies of this Macro-Model for use within
their company only.
This Macro-Model is provided “AS IS, WHERE IS, AND WITH NO
WARRANTY OF ANY KIND EITHER EXPRESSED OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.”
In no event will Intersil be liable for special, collateral, incidental, or
consequential damages in connection with or arising out of the
use of this Macro-Model. Intersil reserves the right to make
changes to the product and the Macro-Model without prior notice.
100Ω
V_IN
1MΩ
-
+
C_F
-2.5V
V_OUT
R_L
FIGURE 47. HIGH GAIN, PRECISION DC-COUPLED AMPLIFIER
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FN6957.6
October 14, 2014